Electrochromism describes the induction of a color change in a medium as a result of charge transfer or electron transfer caused by an externally applied potential. The color changes are indications of induced chemical changes in the species of interest. For most chemical species exhibiting this effect, the change is from one color to another.
The prior art in this field is set forth in my previously issued U.S. Pat. No. 4,386,792 and pending application Ser. No. 858,384 filed May 1, 1986 and Ser. No. 180,399 filed Apr. 12, 1988.
The prior invention embodied an electronic display element useful in electronic color display devices. Broadly, that invention comprised two electrodes, at least one electrode being transparent. A thin film of polymeric aniline or its chemical derivatives was electrolytically plated on one electrode using an acidic solution containing the monomeric aniline. After the polymer film was coated, the solution was replaced by an electrolyte which did not contain the aniline monomer. The electrolyte plated the other electrode and interfaced with the polyaniline.
The electrolytic process for plating the aniline and electrolyte material is time consuming and energy intensive. Further, it is difficult to uniformly plate large non-planar surfaces, such as the wall of an existing building.
It would be desirable to coat the electrochromic material non-electrochemically on the electrode by brushing, spraying, dipping, screen printing, etcetera.
This invention broadly embodies an electrodeless process of coating the electrochromic polymer on an electrode or surface. The aniline monomer is polymerized and coated as polyaniline in thin film form on a substrate.
The process involves adding a chemical oxidant to a solution of aniline to effect the polymerization of the monomer at an electrode surface to form a layer of electrochromic material. In the preferred embodiment a catalyst is used to enhance the affinity and adhesion of the polymer to the surface. This method, therefore, combines the polymerization of the monomer and the coating of the thin film of the electrochromic polymer on an electrode without the use of electrolysis. A polymer electrolyte is then coated on or a polymer electrolyte film is placed in ion transfer relationship with the electrochromic polymer and an electrode.